1. Field of the Invention
The present invention generally relates to a compressor, and more particularly, it relates to a cylinder assembly of a hermetic compressor which is installed in appliances like refrigerators to compress refrigerant.
2. Description of the Prior Art
Referring to FIGS. 1 and 2, a conventional hermetic compressor 100 includes a casing 110 having a refrigerant inflow pipe 111 and a refrigerant outflow pipe (not shown) provided therein, an electronically-driven unit 120 and a cylinder assembly 130.
The electronically-driven unit 120 supplies driving force for refrigerant compression, and includes a stator 120 fixed inside of the casing 110, a rotor rotating in the stator 121 and having a rotary shaft 125 force fit therein, an eccentric unit 127 eccentrically connected to one end of the rotary shaft 125, and a piston 129 connected to a side of the eccentric unit 127.
The cylinder assembly 130 is provided to compress refrigerant flowing into the compressor 100, and includes a cylinder block 131 having a cylinder 133, i.e., a space for permitting reciprocal movement of the piston 129, formed therein, a cylinder head 135 formed on an open side of the cylinder block 131 to seal the cylinder 133, a valve plate 137 disposed between the cylinder block 131 and the cylinder head 135, and a cylinder gasket 136.
The cylinder head 135 has a partition 135c formed therein, which defines a space between the valve plate 137 and the cylinder head 135 into a refrigerant suction chamber 135a and a refrigerant discharge chamber 135b. The refrigerant suction chamber 135a temporarily reserves the refrigerant which is flowing to the cylinder 133 through the refrigerant inflow pipe 111, and the refrigerant discharge chamber 135b temporarily accommodates the refrigerant compressed by the cylinder 133.
The valve plate 137 includes a refrigerant suction hole 137a for interconnecting the cylinder 133 and the refrigerant suction chamber 135a, and a refrigerant discharge hole 137c for interconnecting the cylinder 133 and the refrigerant discharge chamber 135b. 
The refrigerant suction hole 137a is opened and closed by a resilient movement of the suction valve 134a that is moved by the flow of refrigerant. The suction valve 134a is formed by cutting off a part of a suction valve sheet 134 disposed in between the cylinder block 131 and the valve plate 137.
As shown in FIG. 3, the refrigerant discharge hole 137c is opened and closed by the resilient movement of the discharge valve 139a that is moved by the flow of refrigerant. The discharge valve 139a is formed on a side of the valve plate 137 that is exposed to the refrigerant discharge chamber 135b, in a manner of covering the refrigerant discharge hole 137c. With one end being secured to the valve plate 137 by a fastening means S such as a rivet, the discharge valve is formed on the valve plate 137 in a cantilever pattern. The free end of the valve plate 137 covers the refrigerant discharge hole 137c. The valve plate 137 has a stopper member 139b and a keeper plate 139c for covering the discharge valve 139, so as to restrict the movement of the discharge valve 139a during refrigerant discharge.
In the conventional hermetic compressor 100 constructed as above, the discharge valve 139a, the stopper member 139b, and the keeper plate 139c have to be separately formed and then assembled onto valve plate 137. Accordingly, a number of parts and complication increases for the manufacturing of the compressors.
Further, as the discharge valve 139a is made of a resilient material and formed in a cantilever pattern, the free end of the discharge valve 139a, which is more apt to be moved than the other parts, usually beats the stopper member 139b and the valve plate 137 during the suctioning/discharging of the refrigerant, resulting in considerable level of noise and vibration. Such generated noise and vibration are further worsened during the movement of the discharge valve 139a due to vibration of the free end. Accordingly, the compressor 100 is operated with a considerable noise, and when used for a long time, the compressor 100 has a problem of deteriorated durability due to vibration resulting in fatigue failures such as a crack in the fastening means S or the like.
Further, since the discharge valve 139a is connected to the valve plate 137 by the separate fastening means S, it is possible that the fixed ends of the valve plate 137 and the discharge valve 139a are pressed to each other inaccurately due to manufacturing errors, or the like. When this happens, as the refrigerant discharge hole 137c is incompletely sealed by the discharge valve 139a, a so-called ‘back flow’ phenomenon occurs, in which discharged refrigerant flows back into the cylinder 133. As a result, the efficiency of the compressor 100 deteriorates.